Aluminum alloy brazing sheet for use in vacuum brazing

ABSTRACT

The present invention relates to an Al alloy brazing sheet for use in vacuum brazing, which is applied to manufacture a heat exchanger having a tank portion and a refrigerant passage respectively formed by bonding press-formed brazing sheets together by means of vacuum brazing. The brazing sheet includes an Al alloy core material having a composition consisting of 0.5 to 2.0 mass % (hereinafter abbreviated simply as %) of Mn, 0.1 to 1.0% of Cu, 0.05 to 0.5% of Mg and 0 to 0.3%. of Ti, with the remainder being Al and inevitable impurities. An Al--Si--Mg alloy brazing filler metal or an alloy brazing filler metal prepared by further adding 0.05 to 1.0% of Sn to the Al--Si--Mg alloy brazing filler metal, is clad on both surfaces of the sheet to a thickness of 5 to 20% the total sheet thickness. An intermediate layer consisting of an Al alloy having a composition consisting of 0.5 to 2.0% of Mn, 0.05 to 0.5% of Mg and 0 to 0.3% of Ti, with the remainder being Al and inevitable impurities, is provided between the core material and the brazing filler metal corresponding to the outside of the tank portion and the refrigerant passage and has a thickness of 30 μm or more, preferably 80 μm or more, and 35% or less of the total sheet thickness. This Al alloy brazing sheet provides excellent outside corrosion resistance for the heat exchanger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an Al alloy brazing sheet which is excellentin corrosion resistance and is suitably used for assembling an Al alloyheat exchanger or the like for automobiles and various industrialpurposes by bonding with brazing, particularly, vacuum brazing.

Incidentally, in this specification, the components of an Al alloy areall expressed by mass percent, which will be hereinafter abbreviatedsimply as %.

2. Description of the Prior Art

Brazing is effective in manufacturing an Al alloy structure of acomplicated shape. In particular, vacuum brazing is extensively used,since this method requires no flux and is free from any environmentalpollution problems. The vacuum brazing uses a brazing sheet in which oneor both surfaces of a core material consisting of Al or Al alloy areclad with an Al alloy brazing filler metal as a cladding material. Withthis method, the brazing sheet is press-formed into members of variousshapes, and these members are assembled in a predetermined structuresuch as a heat exchanger, for instance, which is then brazed by heatingin a vacuum.

As for a brazing sheet for use in vacuum brazing, various Al alloys fora core material and various Al alloy brazing filler metals for acladding material have been developed. At present, these materials arestandardized by JIS-Z-3263 and JIS-H-4000.

In the case of an ordinary brazing sheet for use in vacuum brazing tomanufacture a heat exchanger, JIS 3003 alloy (including, as a typicalalloy, Al--Cu--Mn alloy with Cu content of 0.15% and Mn content of1.1%), JIS 3005 alloy (including, as a typical alloy, Al--Mn--Mg alloywith Mn content of 1.1% and Mg content of 0.4%) and JIS 3105 alloy(including, as a typical alloy, Al--Mn--Mg alloy with Mn content of 0.6%and Mg content of 0.6%) are used for the core material, while JIS 4004alloy brazing filler metal (including, as a typical material, Al--Si--Mgalloy with Si content of 10% and Mg content of 1.5%) and JIS 4104 alloybrazing filler metal (including, as a typical material, Al--Si--Mg--Bialloy with Si content of 10%, Mg content of 1.2% and Bi content of 0.1%)are used for the cladding material. The brazing sheet has a thickness ofabout 0.3 to 1.5 mm, and one or both surfaces of the core material areclad with a brazing filler metal having a thickness 5 to 15% per side ofthe total thickness.

Such a brazing sheet is manufactured into an Al alloy heat exchangerhaving a hollow structure such as an evaporator of drawn-cup type, anoil cooler or a radiator. An evaporator so drawn-cup type 10 as shown inFIG. 4 for instance, is manufactured as follows. A brazing sheet, inwhich both surfaces of the above Al alloy core material are clad withthe above Al alloy brazing filler metal, is manufactured into arefrigerant passage constituent member 1 as shown in FIGS. 2 and 3 bymeans of press-forming, and this member 1 is arranged in layers as shownin FIG. 4. Then, corrugated fins 2 are attached between the layeredmembers 1, and side plates 6, 6', a refrigerant inlet pipe 7 and arefrigerant outlet pipe 8 are arranged and assembled into a core whichis then brazed in a vacuum. Brazing in this case is carried out byheating up to about 873K in a vacuum of about 1.3×10³ to 1.3×10⁻² Pa.

With a tendency to reduce the weight of automobiles, there have beendemands that the thickness of materials for their heat exchangers shouldbe reduced. On the other hand, automobiles are used in a variety ofenvironments, and therefore, need materials which can withstand thevarious conditions encountered by automobiles. In particular, in case ofa heat exchanger of drawn-cup type having no sacrificial layer,corrosion resistance of a core material of a brazing sheet is the mostimportant characteristic. Thus, it is desirable to develop corrosionresistant brazing sheets.

The corrosion resistance of a brazing sheet is related to thedistribution of alloying elements across the thickness of the material.However, alloying elements such as Cu and Zn, which are effective incorrosion resistance of a material, are distributed to be symmetricalwith each other on the sheet surface side and its reverse side about thecenter of the sheet thickness when heating for brazing is carried out.Therefore, when the surface of a brazing sheet causes pitting corrosion,a material, which makes progress of pitting corrosion on the surfaceside slower than that at the center of the thickness, startsacceleration of pitting corrosion subsequent to that at the center ofthe thickness. Thus, it is not too much to say that a portioncorresponding to half of the thickness makes a contribution to theimprovement of corrosion resistance. Improvement of penetration life byadding alloying elements to a core material has its limit.

Since Cu added makes the potential of aluminum noble, Cu is added to thecore material of a brazing sheet for the purpose of improving thecorrosion resistance. However, Cu added to the core material is diffusedinto a brazing filler metal which has melted in heating for brazing. Cufurther forms an eutectic and is concentrated when the brazing fillermetal is solidified after heating for brazing. Therefore, the more Cuthe core material of a brazing sheet contains, the more the corrosion ofa layer resulting from resolidifying the brazing filler metal isaccelerated. Accordingly, the quantity of alloying elements such as Cuadded to the core material of the brazing sheet is limited for theimprovement of corrosion resistance.

Conventionally, a four or five-layer brazing sheet having anintermediate layer between a core material and a brazing filler metalhas been used for the purpose of preventing alloying elements of thebrazing filler metal from being diffused into the core material, orpreventing alloying elements of the core material from being diffusedinto the brazing filler metal in heating for brazing. For instance,brazing sheets disclosed in Japanese Patent Toku-Kai-Hei 2-30394,1-208432 and 5-65582 or the like correspond to such a four or five-layerbrazing sheet.

However, these brazing sheets as disclosed above do not sufficientlyimprove the exterior corrosion resistance of a heat exchanger (i.e., anevaporator of drawn-cup type or the like).

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the exterior sidecorrosion resistance of a heat exchanger by solving the above problemswhich occur when a brazing sheet is manufactured into a heat exchangerby means of vacuum brazing. More specifically, its object is to providean Al alloy brazing sheet which has excellent exterior side corrosionresistance.

The present inventors have studied exterior side corrosion resistance ofa heat exchanger with a view toward solving the above problems, and as aresult, they have discovered that an intermediate layer should beprovided between a brazing filler metal and a core material to preventalloying elements of the brazing filler metal from being diffused intothe core material and to prevent alloying elements (i.e., Cu or thelike) of the core material from being diffused into the brazing fillermetal in heating for brazing, and the alloy composition, thickness andthe percentage of the total thickness of the intermediate layer arelargely related to the corrosion resistance of a brazing sheet and areimportant to the corrosion resistance of the brazing sheet.

In order to attain the above object, a first embodiment of the presentinvention relates to an Al alloy brazing sheet for use in vacuumbrazing, which is applied to manufacture a heat exchanger having a tankportion and a refrigerant passage respectively formed by bondingpress-formed brazing sheets together by means of vacuum brazing, andcomprises an Al alloy core material having a composition consisting of0.5 to 2.0% of Mn, 0.1 to 1.0% of Cu, 0.05 to 0.5% of Mg and 0 to 0.3%of Ti, with the remainder being Al and inevitable impurities, anAl--Si--Mg alloy brazing filler metal, with which both surfaces of theAl alloy core material are clad to 5 to 20% of the total thickness ofthe sheet, and an intermediate layer consisting of an Al alloy having acomposition consisting of 0.5 to 2.0% of Mn, 0.05 to 0.5% of Mg and 0 to0.3% of Ti, with the remainder being Al and inevitable impurities,wherein the intermediate layer is provided between the core material andthe brazing filler metal corresponding to the outer surface of the tankportion and that of the refrigerant passage, and the intermediate layerhas a thickness of 30 μm or more and 35% or less of the total thickness.

A second embodiment of the present invention relates to an Al alloybrazing sheet for use in vacuum brazing, which is applied to manufacturea heat exchanger having a tank portion and a refrigerant passagerespectively formed by bonding press-formed brazing sheets together bymeans of vacuum brazing, and comprises an Al alloy core material havinga composition consisting of 0.5 to 2.0% of Mn, 0.1 to 1.0% of Cu, 0.05to 0.5% of Mg and 0 to 0.3% of Ti, with the remainder being Al andinevitable impurities, an Al--Si--Mg alloy brazing filler metal, withwhich both surfaces of the Al alloy core material are clad to 5 to 20%,per side, of the total thickness, and an intermediate layer consistingof an Al alloy having a composition consisting of 0.5 to 2.0% of Mn,0.05 to 0.5% of Mg, 0 to 0.3% of Ti and one or both of 0.05 to 0.5% ofSn and 0.05 to 10.0% of Zn, with the remainder being Al and inevitableimpurities, wherein the intermediate layer is provided between the corematerial and the brazing filler metal corresponding to the outer surfaceof the tank portion and the refrigerant passage, and the intermediatelayer has a thickness of 30 μm or more and 35% or less of the totalthickness.

A third embodiment of the present invention is preferable to the firstand second embodiments of the present invention, and relates to an Alalloy brazing sheet for use in vacuum brazing, in which the thicknessand percentage total thickness of the intermediate layer in the firstand second embodiments of the present invention are, respectively, 80 μmor more and 35% or less.

Further, a fourth embodiment of the present invention relates to an Alalloy brazing sheet for use in vacuum brazing, in which 0.05 to 1.0% ofSn is further added to the Al--Si--Mg alloy brazing filler metal in thefirst and second embodiments of the present invention.

Hereinafter will be described the present invention in detail.

(1) First Embodiment

A description will now be given of the Al alloy brazing sheet accordingto the first embodiment of the present invention.

(i) Core Material

A description will now be given of the functions of alloying elementsadded to an Al alloy used for the core material of the brazing sheet andthe reasons for the ranges given.

0.1 to 1% of Cu is added for improving the corrosion resistance. Cucontent less than its lower limit does not show its satisfactoryeffects. On the other hand, Cu content more than its upper limit easilycauses intergranular corrosion, and also increases the quantity ofbrazing filler metal diffused into the core material, resulting indegradation of corrosion resistance. Accordingly, Cu content is limitedto 0.1 to 1.0%, preferably to 0.15 to 0.5%.

0.5 to 2.0% of Mn is added for enhancing the strength. Mn content lessthan its lower limit is less effective in enhancing the strength. On theother hand, Mn content more than its upper limit increases the quantityof brazing filler metal diffused into the core material in heating forbrazing, resulting in degradation of brazing properties and corrosionresistance. Accordingly, Mn content is limited to 0.5 to 2.0%,preferably to 0.8 to 1.5%.

0.05 to 0.5% of Mg is added for enhancing the strength. Mg content lessthan its lower limit is less effective in enhancing the strength. On theother hand, Mg content more than its upper limit increases the quantityof brazing filler metal diffused into the core material in heating forbrazing, resulting in degradation of brazing properties and corrosionresistance. Accordingly, Mg content is limited to 0.05 to 0.5%,preferably to 0.1 to 0.3%.

0 to 0.3% of Ti is added for improving the corrosion resistance. Themeaning of the range of 0 to 0.3% is as follows. Namely, 0% (i.e. lessthan 0.01%) means that Ti is not added at all. Ti content is limited to0.01 to 0.3% when added. Ti content more than 0.3% produces coarse Ticrystal, and damages the corrosion resistance. Accordingly, Ti contentis limited to 0 to 0.3%. Whether or not Ti is to be added is decidedaccording to the intended use of the product. Incidentally, Ti contentis preferably limited to about 0.05 to 0.20% when added.

Other alloying elements contained in the core material includeinevitable impurities such as Si, Fe, Cr and Zn. If the contents ofthese impurities are respectively within the normal tolerance, namely,Si, Fe, Cr and Zn contents are respectively regulated to be 0.6% orless, 0.7% or less, 0.20% or less and 0.40% or less, no problems needarise. However, each of the Si and Fe contents is preferably regulatedto be 0.20% or less.

(ii) Material of Intermediate Layer

A description will now be given of the alloying elements added to the Alof the intermediate layer material of the Al alloy brazing sheetaccording to the present invention and the reasons why the contentsthereof are limited to the specified ranges.

0.5 to 2.0% of Mn is added for enhancing the strength. Mn content lessthan its lower limit is less effective in enhancing the strength. On theother hand, Mn content more than its upper limit increases the quantityof brazing filler metal diffused into the core material in heating forbrazing, resulting in degradation of brazing properties and corrosionresistance. Accordingly, Mn content is limited to 0.5 to 2.0%,preferably to 0.8 to 1.5%.

0.05 to 0.5% of Mg is added for enhancing the strength. Mg content lessthan its lower limit is less effective in enhancing the strength. On theother hand, Mg content more than its upper limit increases the quantityof brazing filler metal diffused into the core material in heating forbrazing, resulting in degradation of brazing properties and corrosionresistance. Accordingly, Mg content is limited to 0.05 to 0.5%,preferably to 0.1 to 0.3%.

0 to 0.3% of Ti is added for improving the corrosion resistance. Themeaning of the range of 0 to 0.3% is as follows. Namely, 0% (i.e., lessthan 0.01%) means that Ti is not added at all. Ti content is limited to0.01 to 0.3% when added. Ti content more than 0.3% produces coarse Ticrystal, and damages the corrosion resistance. Accordingly, Ti contentis limited to 0 to 0.3%, preferably to 0.05 to 0.2% when added.

If Cu is added to the intermediate layer, Cu is diffused from theintermediate layer into the brazing filler metal on the outer side inheating for brazing. When the brazing filler metal is solidified, Cucomes into an eutectic part and is concentrated, resulting indegradation of corrosion resistance. Accordingly, Cu is not added to theintermediate layer at all.

Other alloying elements in the Al alloy material of the intermediatelayer include inevitable impurities such as Si, Fe, Cr, Zn and Cu. Ifthe contents of these impurities are respectively within the normaltolerance, i.e., Si, Fe, Cr, Zn and Cu contents are respectivelyregulated to be 0.6% or less, 0.7% or less, 0.20% or less, 0.40% or lessand 0.05% or less, no problems need arise relative to workability andcorrosion resistance or the like. However, each of Si and Fe contents ispreferably regulated to be 0.20% or less.

According to the brazing sheet of the present invention, theintermediate layer consisting of the above Al alloy is provided on oneside of the core material, namely, on the side corresponding to theoutside of a tank portion and a refrigerant passage of a heat exchanger.Further, the intermediate layer is clad with the brazing filler metal.

Ordinarily, the other surface of the core material is directly clad withthe brazing filler metal, but not in all cases.

The intermediate layer is provided on the side corresponding to theoutside of the tank portion and the refrigerant passage, since theoutside of the tank portion and the refrigerant passage should withstanda more severe corrosive environment.

The thickness of the intermediate layer of the Al alloy brazing sheetaccording to the present invention is set to be 30 μm or more. When thethickness of the intermediate layer is less than 30 μm, Cu contained inthe core material is diffused into the brazing filler metal through theintermediate layer in heating for brazing. When the brazing filler metalmelts and is solidified, Cu diffused into the brazing filler metal comesinto an eutectic portion and is concentrated, resulting in degradationof corrosion resistance.

The thickness of the intermediate layer is set to be 35% or less of thetotal thickness. When the thickness of the intermediate layer relativeto the total thickness is too large, the strength of the material isdegraded to make it hard to press-form the material. Further, in thiscase, a portion which provides sacrificial corrosion prevention of thecore material becomes too large, and when the corrosion is in theadvanced stage, the remaining sheet thickness becomes too small to standthe internal pressure required of a heat exchanger. Accordingly, thethickness of the intermediate layer is set to be 30 μm or more and 35%or less of the total thickness.

(iii) Al--Si--MQ Alloy Brazing Filler Metal

The brazing filler metal used in the present invention is notparticularly limited. Use may be made of an Al--Si--Mg alloy brazingfiller metal normally applied to vacuum brazing, such as JIS 4004 alloybrazing filler metal (including Al--Si--Mg alloy with Si content of 10%and Mg content of 1.5%, a typical alloy composition) and JIS 4104 alloybrazing filler metal (including Al--Si--Mg--Bi alloy with Si content of10%, Mg content of 1.2%, and Bi content of 0.1%, a typical alloycomposition).

Further, a normal thickness, i.e., a thickness of 5 to 20% per siderelative to the total thickness may be used for the brazing fillermetal.

In the present invention, both surfaces of the sheet are clad with thebrazing filler metal.

(iv) Sectional Structure of Brazing Sheet

The Al alloy brazing sheet according to the present invention isconstituted as described above, and has the sectional structure as shownin FIG. 1.

Namely, this brazing sheet has a four-layer structure, in which the sideC of the Al alloy core material 5 corresponding to the outside of thetank portion and the refrigerant passage of the heat exchanger is cladwith a brazing filler metal 3 through an intermediate layer 4 consistingof the above Al alloy, and the other side D (i.e., the sidecorresponding to the inner surface) of the core material 5 is clad witha brazing filler metal 3'.

(2) Second Embodiment

A description will now be given of the Al alloy brazing sheet accordingto the second embodiment of the present invention.

The Al alloy brazing sheet according to the second embodiment of thepresent invention has similar characteristics, i.e., the composition ofthe core material, the thickness of the intermediate layer material, thecomposition of the brazing filler metal and the structure of the sheetand the like as those of the first embodiment, except that the Al alloyof the intermediate layer material has a composition consisting of 0.5to 2.0% of Mn, 0.05 to 0.5% of Mg, 0 to 0.3% of Ti, and one or both of0.05 to 0.5% of Sn and 0.05 to 10.0% of Zn, with the remainder being Aland inevitable impurities.

As the result of further adding one or both of Sn and Zn, in addition tothe Mn, Mg and Ti of the first embodiment, the Al alloy of theintermediate layer material according to the second embodiment furtherimproves the corrosion resistance of the brazing sheet.

0.05 to 0.5% of Sn is added for improving the corrosion resistance of amaterial by making the potential less noble to improve sacrificialcorrosion resistance of the core material. Sn content less than itslower limit is less effective in improving the corrosion resistance. Onthe other hand, Sn content more than its upper limit degrades the selfcorrosion resistance of the intermediate layer. Accordingly, Sn contentis limited to 0.05 to 0.5%, preferably to 0.05 to 0.2%.

0.05 to 10.0% of Zn is added for improving the corrosion resistance of amaterial by making the potential less noble to improve sacrificialcorrosion resistance of the core material, similarly to the case of Sn.Zn content less than its lower limit is less effective in improving thecorrosion resistance. On the other hand, Zn content more than its upperlimit degrades the self corrosion resistance of the intermediate layer.Accordingly, Zn content is limited to 0.05 to 10.0%, preferably to 3.0to 6.0%.

Incidentally, one or both of elemental Sn and Zn are added. Althoughonly one of Sn and Zn may have the effect of improving the corrosionresistance, it may be good to add both of Sn and Zn simultaneously.

(3) Third Embodiment

The third embodiment of the present invention is preferable to the firstand second embodiments of the present invention regarding the thicknessof the intermediate layer material.

Namely, the third embodiment of the present invention is an Al alloybrazing sheet, in which the thickness of the intermediate layer is 80 μmor more and 35% or less of the total thickness.

The intermediate layer is set to have a thickness of 80 μm or more and35% or less of the total thickness, to provide excellent corrosionresistance.

(4) Fourth Embodiment

The fourth embodiment of the present invention is an Al alloy brazingsheet, in which 0.05 to 0.5% of Sn is further added to the Al--Si--Mgalloy brazing filler metal of the Al alloy brazing sheet in the first tothird embodiments of the present invention to further improve thecorrosion resistance.

Sn comes into an eutectic portion when the brazing filler metal issolidified after heating for brazing. Thus, Sn neutralizes the potentialof the eutectic and makes it possible to further improve the corrosionresistance of the surface of the brazing sheet after heating forbrazing.

Sn content less than its lower limit does not show its satisfactoryeffects. On the other hand, Sn content more than its upper limitdegrades the corrosion resistance of the brazing sheet surface afterheating for brazing, resulting in acceleration of corrosion.Accordingly, Sn content is limited to 0.05 to 05%, preferably to 0.05 to0.2%.

Incidentally, in the case of adding Sn (0.05 to 0.5%) to the Al--Si--Mgalloy brazing filler metal in the present invention, it is sufficient toadd Sn to the brazing filler metal on the side of the intermediatelayer. Otherwise, Sn may be added to the brazing filler metals on bothsides of the core material according to circumstances in manufacturing.

Other characteristics of the fourth embodiment of the present inventionare similar to those of the first to third embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the invention willbecome apparent from the following description of preferred examples ofthe invention with reference to the accompanying drawings, in which:

FIG. 1 is a view showing the sectional structure of an Al alloy brazingsheet according to the present invention;

FIG. 2 is a plan view showing a refrigerant passage forming member foran evaporator of drawn-cup type in the prior art;

FIG. 3 is a sectional view taken along line B--B' in FIG. 2; and

FIG. 4 is a schematic sectional view showing a heat exchanger (i.e., anevaporator of drawn-cup type) of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

1 Alloy Compositions of Core Material and Intermediate Layer Material

Various core materials and various intermediate layer materialsrespectively having the different alloy compositions shown in table 1were prepared. These core materials and intermediate layer materialswere combined together as shown in Table 1. One surface of each corematerial was clad with the intermediate layer material, and bothsurfaces of this clad material were clad with a brazing filler metalconsisting of JIS 4104 alloy (to a thickness of 15% per side relative tothe total thickness). In this case, the thickness of the intermediatelayer was 15% of the total thickness.

The clad materials formed in this manner were soaked hot-rolled,intermediate-annealed, and cold-rolled into brazing sheets of 1.0 mm inthickness according to a normal method. Table 1 shows the constitutionof these brazing sheets.

The brazing sheets (Nos. 1 to 16) thus formed as shown in Table 1 werecleaned, finally annealed, and thereafter manufactured into samples byheating for vacuum brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³Pa.

A corrosion test (CASS test) was conducted with one surface (i.e., theside denoted by D in FIG. 1) of each sample coated with resin, and theother surface (i.e., the side denoted by C in FIG. 1) on the side of theintermediate layer remained exposed. These samples were taken out aftera lapse of 500 hours and a lapse of 1000 hours from start of the test.Then, after a corrosion product was removed from the surface of eachsample, the conditions of corrosion of the materials were evaluated. Theevaluation was performed by measuring the maximum depth of pit corrosionwith an optical microscope according to focal depth measurement. As forsome materials, the types of corrosion were examined as observed in asection. Table 1 also shows the results of measurement.

                                      TABLE 1                                     __________________________________________________________________________             Brazing sheet                                                                                    Intermediate layer material (with                   Core material alloy component which one surface of core material is                                     clad)                                               (mass %) Alloy component (mass %)                                                 No.                                                                              Si                                                                              Fe                                                                              Cu Mn                                                                              Mg                                                                              Ti Al   Si                                                                              Fe                                                                              Cu Mn                                                                              Mg Ti Al                                 __________________________________________________________________________      Example of 1 0.1 0.2 0.0 1.0 0.1 0.15 Remainder 0.1 0.2 --  1.0  0.08                                                  0.15 Remainder                       the present 2 0.1 0.2 0.1 1.0 0.1 -- Remainder 0.1 0.2 -- 1.2 0.1 0.15                                                 Remainder                            invention 3 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                     Remainder                             4 0.1 0.2 0.3 1.0 0.2 0.15 Remainder 0.1 0.2 -- 1.0 0.2 0.15 Remainder        5 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 -- Remainder                                                      6 0.2 0.0 0.15 1.0 0.2 0.15                                                 Remainder 0.2 0.0 -- 0.5 0.1                                                  0.15 Remainder                        7 0.2 1.6 0.15 1.0 0.2 0.15 Remainder 0.2 0.0 -- 0.1 0.3 -- Remainder                                                   8 0.1 0.2 0.3 1.0 0.2 --                                                    Remainder 0.1 0.2 -- 0.0 0.1                                                  -- Remainder                          9 0.1 0.2 0.5 1.0 0.2 -- Remainder 0.1 0.2 -- 0.0 0.1 -- Remainder                                                      10 0.2 0.0 0.15 1.0 0.2 0.15                                                Remainder 0.1 0.2 -- 0.0 0.2                                                  -- Remainder                          11 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 0.0 0.3 -- Remainder                                                     12 0.1 0.2 0.5 1.0 0.2 --                                                   Remainder 0.1 0.2 -- 0.0 0.2                                                  -- Remainder                         Comparative 13 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.2 0.3 0.15 -- -- --                                                  Remainder                            example 14 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                    Remainder                             15 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 0.1S Remainder                                                   16 0.1 0.2 1.2 1.0 0.1 --                                                   Remainder 0.1 0.2 -- 1.0 0.1                                                  0.1S Remainder                     __________________________________________________________________________                       Brazing sheet    Corrosion resistance                                         Intermediate layer material                                                                    Maximum depth of pit                        (with which one surface  corrosion (μm)                                                     of core material is clad)                                                                      After lapse                                                                         After lapse                                                  Clad       of 500 hrs                                                                          of 1000 hrs                             Clad thickness Brazing from start from start                                 No. thickness % (μm) alloy No. of test of test                          __________________________________________________________________________      Example of 1 15 150 4104 250 300                                              the present 2 15 150 4104 240 280                                             invention 3 15 150 4104 220 270                                                4 15 150 4104 350 390                                                         5 15 150 4104 330 350                                                         6 15 150 4104 390 420                                                         7 15 150 4104 370 400                                                         8 15 150 4104 320 370                                                         9 15 150 4104 230 290                                                         10 15 150 4104 270 390                                                        11 15 150 4104 300 370                                                        12 15 150 4104 290 350                                                       Comparative 13 15 150 4104 620 Penetration                                    example 14 15 150 4104 610 Penetration                                         15 15 150 4104 690 Penetration                                                16 15 150 4104 Penetration Penetration                                     __________________________________________________________________________     Note:                                                                         In Tables 1 to 6,                                                             1) Si and Fe are contained as impurities in core material and -- in Ti        represents Ti content less than 0.01 mass %                                   2) Si, Fe and Cu are contained as impurities in intermediate layer            material, -- in Cu and -- of Ti respectively represent Cu content less        than 0.02 mass % and Ti content less than 0.01 mass %, and                    3)Both surfaces of sheet are clad with brazing alloy (at clad rate of 15%     per side to total thickness).                                            

As is apparent from Table 1, the brazing sheets (Nos. 1 to 12) accordingto the present invention are superior in corrosion resistance to thebrazing sheets of comparative examples (Nos. 13 to 16).

2 Thickness of the Intermediate Layer

The core material of No. 3 in Table 1 was clad with the intermediatelayer material of No. 3 in Table 1 with the cladding thickness of theintermediate layer material varied in the range of 2 to 40%, and bothsurfaces of the clad material were further clad with a brazing fillermetal consisting of JIS 4104 alloy (15% per side relative to the totalthickness).

The clad materials formed in this manner were soaked, hot-rolled,intermediate-annealed and cold rolled into brazing sheets of 1.0 mm inthickness and 0.5 mm in thickness, respectively, according to a normalmethod. Table 2 shows the constitution of these brazing sheets.

The brazing sheets (Nos. 3, 17 to 34) shown in Table 2 were cleaned,finally annealed, and thereafter manufactured into samples by heatingfor brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³ Pa.

These samples were further manufactured into test pieces according toJIS No. 5, and the tensile strength of each test piece was measured.

Further, these samples were press-formed. An evaluation was made as towhether or not a press-formed sample had a sufficient height bymeasuring the stretched height of the press-formed sample.

Further, a corrosion test (CASS test) was conducted with one surface ofeach sample coated with resin similarly to the above case. These sampleswere taken out after a lapse of 500 hours and a lapse of 1000 hours fromstart of the test. Then, after a corrosion product was removed from thesurface of each sample, the conditions of corrosion of the material wereevaluated. The evaluation was performed by measuring the maximum depthof pit corrosion with an optical microscope according to focal depthmeasurement. Table 2 also shows the results of measurement.

                                      TABLE 2                                     __________________________________________________________________________             Brazing sheet                                                                                  Intermediate layer material                           (with which one surface of core material is clad)                                    Core material alloy component     Clad                                                                              Clad                             (mass %) Alloy component (mass %) thick- thickness                                No.                                                                              Si                                                                              Fe                                                                              Cu                                                                              Mn                                                                              Mg                                                                              Ti                                                                              Al   Si                                                                              Fe                                                                              Cu                                                                              Mn                                                                              Mg                                                                              Ti                                                                              Al   ness %                                                                            (μm)                        __________________________________________________________________________      Example of  3 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                       Remainder 15 150                 the present 17 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                      Remainder 10 100                 invention 18 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                        Remainder 8 80                    19 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 7                                                     70                                20 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 5                                                     50                                21 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 25                                                    250                               22 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 30                                                    300                               23 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 35                                                    350                               24 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 6                                                     30                                25 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 15                                                    75                                26 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 20                                                    100                               27 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 25                                                    125                               28 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 30                                                    150                               29 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 35                                                    175                              Comparative 30 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                      Remainder 2 20                   example 31 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                          Remainder 40 400                  32 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 2                                                     10                                33 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 5                                                     25                                34 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- Remainder 40                                                    200                            __________________________________________________________________________                                Corrosion resistance                                                                      Reference                                                                           Reference                          Maximum depth of pit Tensile height                                          Brazing sheet corrosion (μm) strength after                                                     Total                                                                              of 500 hrs                                                                          of 1000 hrs                                                                         after press-                              Brazing thickness from start from start heathing forming                     No. alloy No. (mm) of test of test (MPa) (mm)                              __________________________________________________________________________      Example of  3 4104 1.0 230 290 140 8.10                                       the present 17 4104 1.0 210 300 143 8.05                                      invention 18 4104 1.0 210 290 144 7.91                                         19 4104 1.0 220 410 144 7.02                                                  20 4104 1.0 240 450 145 7.01                                                  21 4104 1.0 250 280 135 6.16                                                  22 4104 1.0 260 270 133 6.18                                                  23 4104 1.0 270 270 131 6.19                                                  24 4104 0.5 180 410 145 6.94                                                  25 4104 0.5 200 370 143 7.11                                                  26 4104 0.5 210 270 139 8.06                                                  27 4104 0.5 210 280 136 8.08                                                  28 4104 0.5 220 250 134 8.09                                                  29 4104 0.5 240 270 132 8.11                                                 Comparative 30 4104 1.0 580 Penetration 147 5.99                              example 31 4104 1.0 370 600 126 8.23                                           32 4104 0.5 Penetration Penetration 150 5.91                                  33 4104 0.5 Penetration Penetration 149 6.00                                  34 4104 0.5 Penetration Peoetration 131 8.14                               __________________________________________________________________________

As is apparent from Table 2, the brazing sheets (Nos. 3, 17 to 29)according to the present invention are by no means inferior in strengthto brazing sheets of comparative examples (Nos. 30 to 34), and areexcellent in formability, particularly in corrosion resistance.

3 Sn Added to Al--Si--Mg Alloy Brazing Filler Metal

The various core materials and various intermediate layer materialsshown in Table 3 were combined together, and these core materials wererespectively clad with the intermediate layer materials. Further, bothsurfaces of each clad material were further clad with a brazing fillermetal prepared by further adding 0.05 to 0.6% of Sn to JIS 4104 alloy(with a cladding thickness of 15% per side relative to the totalthickness).

The clad materials formed in this manner were soaked, hot-rolled,intermediate-annealed and cold-rolled into brazing sheets of 1.0 mm inthickness according to a normal method. Table 3 shows the constitutionof these brazing sheets.

These brazing sheets (Nos. 35 to 42) shown in Table 3 were cleaned,finally annealed, and thereafter manufactured into samples by heatingfor vacuum brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³ Pa.

A corrosion test (CASS test) was conducted with one surface of eachsample coated with resin, similarly to the above case. These sampleswere taken out after a lapse of 500 hours and a lapse of 1000 hours fromstart of the test. Then, a corrosion product was removed from thesurface of each sample, and the conditions of corrosion of the materialwere evaluated. The evaluation was performed by measuring the maximumdepth of pit corrosion with an optical microscope according to focaldepth measurement. Table 3 also shows the results of measurement.

                                      TABLE 3                                     __________________________________________________________________________             Brazing sheet                                                                                        Intermediate layer material                     Core material alloy component (with which one surface of core material                                      is clad)                                        (mass %) Alloy component (mass %)                                                 No.                                                                              Si Fe Cu Mn Mg Ti Al   Si Fe Cu Mn Mg Ti Al                          __________________________________________________________________________      Example of 35 0.1 0.2 0.5 1.0 0.1 --  Remainder 0.1 0.2 -- 1.0 0.1 --                                                         Remainder                     the present 36 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                         Remainder                     invention 37 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 --                                                           Remainder                      38 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 -- Remainder                                                            39 0.1 0.6 0.15 1.0                                                         0.2 1.15 Remainder 0.2                                                        0.6 -- 1.0 0.2 --                                                             Remainder                     Comparative 40 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                         Remainder                     example 41 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 --                                                             Remainder                      42 0.1 0.6 0.15 1.0 0.2 1.15 Remainder 0.2 0.6 -- 1.0 0.2 -- Remainder     __________________________________________________________________________                    Brazing sheet              Corrosion resistance                               Intermediate layer material                                                                              Maximum depth of pit                 (with which one surface of  corrosion (μs)                                               core material is clad)     After lapse                                                                         After lapse                                        Clad  Brazing alloy  of 500 hrs                                                                          of 1000 hrs                    Clad thickness Alloy component (mass %) from start from start                            No.                                                                              thickness %                                                                         (μm)                                                                             Si Mg                                                                              Si                                                                              Sn Al   of test                                                                             of test                      __________________________________________________________________________      Example of 35 15 150 10.0 1.5 0.1 0.2 Remainder 100 210                       the present 36 15 150 10.0 1.5 0.1 0.5 Remainder 190 220                      invention 37 15 150 10.0 1.5 0.1  0.05 Remainder 110 240                       38 15 150 10.0 1.5 0.1 0.3 Remainder 180 230                                  39 15 150 10.0 1.5 0.1 0.1 Remainder 100 220                                 Comparative 40 15 150 10.0 1.5 0.1 0.6 Remainder 410 750                      example 41 15 150 10.0 1.5 0.1 0.6 Remainder 520 800                           42 15 150 10.0 1.5 0.1 0.6 Remainder 560 780                               __________________________________________________________________________

As is apparent from Table 3, the brazing sheets (Nos. 35 to 39)according to the present invention have corrosion resistance superior tothat of the brazing sheets of the comparative examples (Nos. 40 to 42).

EXAMPLE 2

1 Alloy Compositions of Core Material and Intermediate Layer Material

Various core materials and various intermediate layer materialsrespectively having different alloy compositions shown in Table 4 wereprepared. These core materials and intermediate layer materials werecombined together as shown in Table 4, one surface of each core materialwas clad with the intermediate layer material, and both surfaces of theclad material were clad with a brazing filler metal consisting of JIS4104 alloy (to a thickness of 15% per side relative to the totalthickness). In this case, the thickness of the intermediate layer wasset to be 15% of the total thickness.

These clad materials formed in this manner were soaked, hot-rolled,intermediate-annealed and cold-rolled into brazing sheets of 1.0 mm inthickness according to a normal method. Table 4 shows the constitutionof these brazing sheets.

These brazing sheets (Nos. 1 to 13) thus formed as shown in Table 4 werecleaned, finally annealed, and thereafter manufactured into samples byheating for vacuum brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³Pa.

A corrosion test (CASS test) was conducted with one surface (i.e., theside denoted by D in FIG. 1) of each sample coated with resin, and theother surface (i.e., the side denoted by C in FIG. 1) on the side of theintermediate layer remained exposed. These samples were taken out aftera lapse of 500 hours and a lapse of 1000 hours subsequent to the startof the test. Then, after a corrosion product was removed from thesurface of each sample, the conditions of corrosion of the material wereevaluated. The evaluation was performed by measuring the maximum depthof pit corrosion with an optical microscope according to focal depthmeasurement. For some materials, the types of corrosion were examined asobserved in section. Table 4 also shows the results of measurement.

                                      TABLE 4                                     __________________________________________________________________________             Brazing sheet                                                                                    Intermediate layer material                         Core material alloy component (with which one surface of core material                                  is clad)                                            (mass %) Alloy component (mass %)                                                 No.                                                                              Si                                                                              Fe                                                                              Cu Mn                                                                              Mg                                                                              Ti Al   Si                                                                              Fe                                                                              Cu Mn                                                                              Mg                                                                              Ti Zn Sn Al                            __________________________________________________________________________      Example of 1 0.1 0.2 0.5 1.0 0.1 --  Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                      -- 0.1  Remainder                                                              the present 2 0.1 0.2                                                        0.5 1.0 0.1 -- Remainder                                                      0.1 0.2 -- 1.0 0.1 -- --                                                      0.15 Remainder                  invention 3 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- 4.0                                                      -- Remainder                     4 0 1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- 4.0 0.15                                                          Remainder                        5 0.1 0.2 0.3 1.0 0.2 1.15 Remainder 0.1 0.2 -- 1.0 0.2 0.15 -- 0.1                                                        Remainder                        6 0.1 0.2 0.3 1.0 0.2 0.15 Remainder 0.1 0.2 -- 1.0 0.2 0.15 4.0 --                                                        Remainder                        7 0.2 0.6 0.15 1.0 0.2 1.15 Remainder 0.2 0.6 -- 1.0 0.2 0.15 -- 0.1                                                       Remainder                        8 0.2 0.2 0.15 1.0 0.2 0.15 Remainder 0.2 0.6 -- 1.0 0.2 -- -- 0.1                                                         Remainder                       Comparative 9 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.2 0.3 0.15 -- -- -- --                                                     -- Remainder                    invention 10 0.1 0.2 1.2 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                       -- -- Remainder                  11 0.1 0.2 0.5 1.0 0.1 0.08 Remainder 0.1 0.2 -- 1.0 0.1 0.15 -- 0.6                                                       Remainder                        12 0.1 0.2 0.5 1.0 0.2 -- Remainder 0.1 0.2 -- 0.8 0.1 -- -- 0.6                                                           Remainder                        13 0.1 0.2 0.5 1.0 0.1 0.08 Remainder 0.1 0.2 -- 1.0 0.1 0.15 12.1 --                                                      Remainder                     __________________________________________________________________________                            Brazing sheet    Corrosion resistance                                         Intermediate layer material                                                                    Maximum depth of pit                   (with which one surface  corrosion (μs)                                                          core material is clad)                                                                         After lapse                                                                         After lapse                                                  Clad       of 500 hrs                                                                          of 1000 hrs                        Clad thickness Brazing from start from start                                 No. thickness % (μs) Alloy No. of test of test                          __________________________________________________________________________      Example of 1 15 150 4104 150 180                                              the present 2 15 150 4104 140 180                                             invention 3 15 150 4104 150 210                                                4 15 150 4104 120 200                                                         5 15 150 4104 180 210                                                         6 15 150 4104 170 240                                                         7 15 150 4104 190 250                                                         8 15 150 4104 150 230                                                        Comparative 9 15 150 4104 620 Penetration                                     invention 10 15 150 4104 Penetration Penetration                               11 15 150 4104 490 Penetration                                                12 15 150 4104 410 Penetration                                                13 15 150 4104 580 Penetration                                             __________________________________________________________________________

As is apparent from Table 4, the brazing sheets (Nos. 1 to 8) accordingto the present invention are more excellent in corrosion resistance thanthe brazing sheets of the comparative examples (Nos. 9 to 13).

2 Thickness of Intermediate Layer

The core material of No. 2 in Table 4 was clad with the intermediatelayer material of No. 2 in Table 2 with the thickness of theintermediate layer material varied in the range of 2 to 40% of the totalthickness, and both surfaces of the clad material ware clad with abrazing filler metal consisting of JIS 4104 alloy (to a thickness of 15%per side relative to the total thickness).

The clad materials formed in this manner were soaked, hot-rolled,intermediate-annealed and cold-rolled into brazing sheets of 1.0 mm inthickness and those of 0.5 mm in thickness according to a normal method.Table 5 shows the constitution of these brazing sheets.

The brazing sheets (Nos. 14 to 31) shown in Table 5 were cleaned,finally annealed and thereafter manufactured into samples by heating forvacuum brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³ Pa.

These samples were manufactured into test pieces according to JIS No. 5,and the tensile strength thereof was measured.

These samples were also press-formed. An evaluation was made as towhether or not a press-formed sample has a sufficient height bymeasuring the stretched height of the press-formed sample.

Further, a corrosion test (CASS test) was conducted with one surface ofeach sample coated with resin similarly to the above case. The sampleswere taken out after a lapse of 500 hours and a lapse of 1000 hourssubsequent to the start of the test. Then, after a corrosion product wasremoved from the surface of each sample, the conditions of corrosion ofthe material were evaluated. The evaluation was performed by measuringthe maximum depth of pit corrosion with an optical microscope accordingto focal depth measurement. Table 5 also shows the results ofmeasurement.

                                      TABLE 5                                     __________________________________________________________________________             Brazing sheet                                                                                  Intermediate layer material                           (with which one surface of core material is clad)                                    Core material alloy component          Clad                                                                              Clad                        (mass %) Alloy component (mass %) thick- thickness                                No.                                                                              Si                                                                              Fe                                                                              Cu                                                                              Mn                                                                              Mg                                                                              Ti                                                                              Al   Si                                                                              Fe                                                                              Cu                                                                              Mn                                                                              Mg                                                                              Ti                                                                              Zn                                                                              Sn Al   ness %                                                                            (μm)                   __________________________________________________________________________      Example of 14 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- --                                                         0.15 Remainder 10 100       the present 15 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 --                                                           -- 0.15 Remainder 8                                                           80                          invention 16 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 7 70                                                             17 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 5 50                                                             18 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 25 250        19 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- -- 0.15                                                              Remainder 30 300                                                                20 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 35 350        21 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- -- 0.15                                                              Remainder 6 30                                                                  22 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 15 75                                                            23 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 20 100        24 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- -- 0.15                                                              Remainder 25 125                                                                25 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 30 150        26 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 -- -- 0.15                                                              Remainder 35 175                                                               Comparative 27 0.1                                                           0.2 0.5 1.0 0.1 --                                                            Remainder 0.1 0.2 --                                                          1.0 0.1 -- -- 0.15                                                            Remainder 2 20                                                                 example 28 0.1 0.2                                                           0.5 1.0 0.1 --                                                                Remainder 0.1 0.2 --                                                          1.0 0.1 -- -- 0.15                                                            Remainder 40 400                                                                29 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 2 10                                                             30 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 5 25                                                             31 0.1 0.2 0.5 1.0                                                          0.1 -- Remainder 0.1                                                          0.2 -- 1.0 0.1 -- --                                                          0.15 Remainder 40         __________________________________________________________________________                                                        200                                                        Corrosion resistance                           Maximum depth of pit Reference: Reference:                                    corrosion (μm) Tensile height                                                                   Brazing sheet                                                                           After lapse                                                                         After strength                                                                            after                                                  Total                                                                              of 500 hrs                                                                          1000 hrs                                                                            after press-                         Brazing thickness from start from start heating forming                      No. alloy No. (mm) of test of test (MPa) (mm)                              __________________________________________________________________________      Example of 14 4104 1.0  90 120 142 7.89                                       the present 15 4104 1.0  80 100 141 7.95                                      invention 16 4104 1.0  65  90 141 7.95                                         17 4104 1.0  70  95 138 8.16                                                  18 4104 1.0 230 260 144 7.65                                                  19 4104 1.0 300 350 145 7.59                                                  20 4104 1.0 340 380 146 7.60                                                  21 4104 0.5 100 200 140 7.93                                                  22 4104 0.5  80 100 143 7.70                                                  23 4104 0.5 100 130 144 7.61                                                  24 4104 0.5 120 135 144 7.90                                                  25 4104 0.5 145 160 145 7.55                                                  26 4104 0.5 160 190 146 7.60                                                 Comparative 27 4104 1.0 350 Penetration 132 8.23                              example 28 4104 1.0 380 500 152 5.67                                           29 4104 0.5 180 Penetration 131 830                                           30 4104 0.5 Penetration Penetration 135 8.11                                  31 4104 0.5 200 300 153 5.60                                               __________________________________________________________________________

As is apparent from Table 5, the brazing sheets (Nos. 14 to 26)according to the present invention are by no means inferior in strengthto the brazing sheets of the comparative examples (Nos. 27 to 31), andare excellent in formability, particularly in corrosion resistance.

3 Sn Added to Al--Si--Mg Alloy Brazing Filler Metal

Various core materials and various intermediate layer materials shown inTable 6 were combined together, and these core materials wererespectively clad with these intermediate layer materials. Further, bothsurfaces of each clad material were clad with a brazing filler metalprepared by adding 0.2 to 1.2% of Sn to JIS 4104 alloy (to a thicknessof 15% per side relative to the total thickness).

The clad materials formed in this manner were soaked, hot-rolled,intermediate-annealed and cold-rolled into brazing sheets of 1.0 mm inthickness according to a normal method. Table 6 shows the constitutionof these brazing sheets.

The brazing sheets (Nos. 32 to 39) shown in Table 6 were cleaned,finally annealed and thereafter manufactured into samples by heating forvacuum brazing at 873K for 3 minutes in a vacuum of 6.7×10⁻³ Pa.

A corrosion test (CASS) test was conducted with one surface of eachsample coated with resin similarly to the above case. The samples weretaken out after a lapse of 500 hours and a lapse of 1000 hourssubsequent to the start of the test. Then, after a corrosion product wasremoved from the surface of each sample, the conditions of corrosion ofthe material were evaluated. The evaluation was performed by measuringthe maximum depth of pit corrosion with an optical microscope accordingto focal depth measurement. Table 6 also shows the results ofmeasurement.

                                      TABLE 6                                     __________________________________________________________________________             Brazing sheet                                                                                    Intermediate layer material                         Core material alloy component (with which one surface of core material                                  is clad)                                            (mass %) Alloy component (mass %)                                                 No.                                                                              Si                                                                              Fe                                                                              Cu Mn                                                                              Mg                                                                              Ti Al   Si                                                                              Fe                                                                              Cu                                                                              Mn                                                                              Mg                                                                              Ti Zn                                                                              Sn Al                              __________________________________________________________________________      Example of 32 0.1 0.2 0.5 1.0 0.1 --  Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                   -- 0.05 Remainder                 the present 33 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                   -- 0.05 Remainder                 invention 34 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 -- --                                                    0.1 Remainder                      35 0.1 0.2 0.15 1.0 0.2 0.15 Remainder 0.1 0.2 -- 1.0 0.2 -- -- 0.1                                                      Remainder                          36 0.1 0.2 0.15 1.0 0.2 0.15 Remainder 0.1 0.2 -- 1.0 0.2 -- -- 0.1                                                      Remainder                         Comparative 37 0.1 0.2 0.5 1.0 0.1 -- Remainder 0.1 0.2 -- 1.0 0.1 0.15                                                   -- 0.05 Remainder                 example 38 0.1 0.2 0.3 1.0 0.2 -- Remainder 0.1 0.2 -- 1.0 0.2 -- --                                                      0.1 Remainder                      39 0.1 0.2 0.15 1.0 0.2 0.15 Remainder 0.1 0.2 -- 1.0 0.2 -- -- 0.1                                                      Remainder                       __________________________________________________________________________                 Brazing sheet             Corrosion resistance                                Intermediate layer material                                                                             Maximum depth of pit                     (with which one surface  corrosion (μm)                                               of core material is clad) After lapse                                                                         After lapse                                         Clad  Brazing alloy of 500 hrs                                                                          of 1000 hrs                        Clad thickness Alloy component (mass %) from start from start                         No.                                                                              thickness %                                                                         (μm)                                                                             Si Mg                                                                              Bi                                                                              Sn                                                                              Al   of test                                                                             of test                          __________________________________________________________________________      Example of 32 15 150 10.0 1.5 0.1 0.2 Remainder 120 140                       the present 33 15 150 10.0 1.5 0.1 0.4 Remainder 190 210                      invention 34 15 150 10.0 1.5 0.1 0.2 Remainder 140 160                         35 15 150 10.0 1.5 0.1 0.2 Remainder 100 130                                  36 15 150 10.0 1.5 0.1 0.4 Remainder 130 160                                 Comparative 37 15 150 10.0 1.5 0.1 1.2 Remainder 650 850                      example 38 15 150 10.0 1.5 0.1 1.2 Remainder 710 Penetration                   39 15 150 10.0 1.5 0.1 1.2 Remainder 580 Penetration                       __________________________________________________________________________

As is apparent from Table 6, the brazing sheets (Nos. 32 to 36)according to the present invention are more excellent in corrosionresistance than the brazing sheets of the comparative examples (Nos. 37to 39).

The present invention remarkably improves the corrosion resistance ofone surface, which one surface must withstand a severe corrosiveenvironment in use, of an Al alloy brazing sheet. Accordingly, in caseof forming this brazing sheet into a heat exchanger, it is possible toremarkably improve the life of the outside corrosion resistance of theheat exchanger.

What is claimed is:
 1. An Al alloy brazing sheet for use in manufacture,by means of vacuum brazing, of a heat exchanger having a tank portionand a refrigerant passage portion, respectively formed by bondingpress-formed brazing sheets together and then vacuum brazing, said Alalloy brazing sheet comprising:an Al alloy core material presentingfirst and second surfaces and having a composition consisting of 0.5 to2.0 mass % hereinafter abbreviated simply as %) of Mn, 0.1 to 1.0% ofCu, 0.05 to 0.5% of Mg and 0.05 to 0.3% of Ti, with the remainder beingAl and inevitable impurities; an intermediate layer presenting opposingsurfaces, one of said opposing surfaces being adhered to said firstsurface of said core material, said intermediate layer consisting of anAl alloy having a composition consisting of 0.5 to 2.0% of Mn, 0.05 to0.5% of Mg and 0.05 to 0.3% of Ti, with the remainder being Al andinevitable impurities, said intermediate layer having a thickness of 30μm or more and constituting 35% or less of the total thickness of thebrazing sheet; and first and second layers of Al--Si--Mg alloy brazingfiller metal adhered, respectively, directly to the other opposingsurface of said intermediate layer to provide an outer surface for theheat exchanger and to said second surface of said core material.
 2. AnAl alloy brazing sheet for use in manufacture, by means of vacuumbrazing, of a heat exchanger having a tank portion and a refrigerantpassage portion respectively formed by bonding press-formed brazingsheets together and then vacuum brazing, said Al alloy brazing sheetcomprising:an Al alloy core material presenting first and secondsurfaces and having a composition consisting of 0.5 to 2.0% of Mn, 0.1to 1.0% of Cu, 0.05 to 0.5% of Mg and 0.05 to 0.3% of Ti, with theremainder being Al and inevitable impurities; an intermediate layerpresenting opposing surfaces, one of said opposing surfaces beingadhered to said first surface of said core material, said intermediatelayer consisting of an Al alloy having a composition consisting of 0.5to 2.0% of Mn, 0.05 to 0.5% of Mg, 0.05 to 0.3% of Ti and one or both of0.05 to 0.5% of Sn and 0.05 to 10.0% of Zn, with the remainder being Aland inevitable impurities, said intermediate layer having a thickness of30 μm or more and constituting 35% or less of the total thickness of thebrazing sheet; and first and second layers of Al--Si--Mg alloy brazingfiller metal each constituting 5-20% of the total thickness of the Alalloy brazing sheet and adhered, respectively, directly to the otheropposing surface of said intermediate layer to provide an outer surfacefor the heat exchanger and to said second surface of said core material.3. An Al alloy brazing sheet for use in vacuum brazing according toclaim 1, wherein the thickness of said intermediate layer is 80 μm ormore and constitutes 35% or less of the total thickness of the Al alloybrazing sheet.
 4. An Al alloy brazing sheet for use in vacuum brazingaccording to claim 1, wherein said Al--Si--Mg alloy brazing filler metalcontains 0.05 to 1.0% Sn.
 5. An Al alloy brazing sheet for use in vacuumbrazing according to claim 2, wherein the thickness of said intermediatelayer is 80 μm or more and constitutes 35% or less of the totalthickness of the Al alloy brazing sheet.
 6. An Al alloy brazing sheetfor use in vacuum brazing according to claim 2, wherein said Al--Si--Mgalloy brazing filler metal contains 0.05 to 1.0% Sn.
 7. An Al alloybrazing sheet for use in vacuum brazing according to claim 3, whereinsaid Al--Si--Mg alloy brazing filler metal contains 0.05 to 1.0% Sn.